1. Field of the Invention
The present invention relates to magnetic field concentration apparatus, particularly signal enhancement and/or apparatus for confining magnetic flux within an aperture, and/or to shield magnetic flux from components, and/or to means for improving signal reception. The present invention has a particular application to passive devices, such as tokens, transponders or smart cards.
2. Prior Art
It is well known that metal placed in the proximity of a magnetic field receiving coil will substantially reduce the amount of magnetic field received by the coil. For example, metal placed between a source of the magnetic field and the coil can operate to prevent any magnetic field from being picked up by the coil as shown in FIG. 1. The metal sheet serves to absorb and deflect the flux radiated from the driver coil or magnetic field source.
FIG. 2 shows another situation where a metal sheet serves to reduce signal reception. The metal sheet is placed behind the coil. The metal sheet acts to reduce the amount of flux received by the coil by radiating an opposing flux field. The closer the metal sheet, to the coil, the larger the opposing flux field and the less signal flux is received by the coil. In effect the metal sheets serve to proportionately nullify the driver coil radiated flux.
U.S. Pat. No. 4,373,163 discloses an electrostatic shield with an antenna loop therein (FIG. 1). The antenna is surrounded by a metal shield. The specification does not disclose a conductor plate proximate and in substantially the same plane as an antenna to enhance signal reception, in accordance with the present invention as will be described in more detail hereinafter.
U.S. Pat. No. 4,486,731 discloses a signal enhancement apparatus in the form of a coil having magnetically permeable material disposed in overlapping relationship with a coil. The coil is influenced by strips 23 and 24 when the coil is oriented parallel to the direction of impinging flux (column 2, lines 23 to 41). However, U.S. Pat. No. 4,486,731 relates to the problem of coil reception the coil is in the same plane as the impinging flux, whereas the present invention relates to increasing the reception of flux by a coil by providing a concentrator in juxtaposition to and in substantially the same plane, as the coil.
U.S. Pat. No. 4,754,284 discloses an automobile antenna system for use in receiving high frequency bands in excess of 50 MHz.